Dangerous pathogens left unsecured at labs across Africa. Halted inspections for mpox, Ebola and other infections at airports and other checkpoints. Millions of unscreened animals shipped across borders.

The Trump administration’s pause on foreign aid has hobbled programs that prevent and snuff out outbreaks around the world, scientists say, leaving people everywhere more vulnerable to threatening viruses and bacteria.

As the reality sets in that the United States is drastically diminishing its foreign assistance to developing countries, an urgent conversation is starting among governments, philanthropists, and global health and development organizations.

It is centered on one crucial question: Who will fill this gap?

Last year, the United States contributed about $12 billion to global health, money that has funded treatment of H.I.V. and prevention of new infections; children’s vaccines against polio, measles and pneumonia; clean water for refugees; and tests and medications for malaria.